1. Field of the Invention
The present invention relates to internal combustion reciprocating engines and in particular to a reduced size internal combustion reciprocating engine of which a plurality can be interconnected to form a larger engine.
2. Description of the Related Art
Internal combustion reciprocating engines have been known for over a century. The internal combustion reciprocating engine has been manufactured in numerous configurations over the years. These engines are utilized in automobiles, air planes and water craft. An important consideration in each of these applications is the size and weight of the engine. There is a trade off between the structural integrity or durability of an engine and the size and weight of the engine. Engine manufacturers design overly massive engine parts to increase the durability and useful life of an engine. Utilization of massive engine parts, however, increases the weight and size of the engine and can actually increase engine wear by increasing the dynamic weight of the moving parts in the engine. Thus there is a need for a reduced weight and size engine that is durable.
Some engine manufacturers have apparently built engines by interconnecting a set of smaller engines or modular engines. Modular engines are known in the prior art as evidenced by the Voorhies patent, U.S. Pat. No. 2,491,630, entitled "An Engine Constructed of Sections Bolted Together Along the Vertical Plane to Form an Entire Head Block and Crankcase Thereof," issued on Dec. 20, 1949. Voorhies patented an internal combustion engine constructed from a series of engine modules. The Voorhies engine however suffers the same inadequacies as other conventional engine designs.
Some of the problems presented by typical engine designs are discussed below.
Cam Followers
Typical cam follower mechanisms act as an intermediary between a cam shaft lobe and a valve stem. Cam followers compensate for rotating cam lobes side thrust. Lobes assert a composite thrust containing both a horizontal (side thrust) and vertical (downward thrust) component. The cam followers absorbs some of the side thrust. Any portion of this horizontal thrust component which is asserted on the valve stem increases wear on the valve stem and valve stem guide in which the valve stem slides. The horizontal and vertical components are asserted upon the cam follower by the rotating cam lobe. The cam lobe rotates, depresses the cam follower mechanism, which in turn depresses the valve stem. Typically a portion of the side thrust component is not compensated for by the cam follower. This side thrust is asserted on the valve stem which increases wear on the valve stem and the valve stem guide.
Typical engine designs typically provide minimal lubrication between the valve stem and the valve stem guide. Inadequate lubrication exacerbates the effect of wear caused by the side thrust asserted on a valve stem by the typical cam follower mechanism. Typically, engine designers utilize long valve stems to provide a relatively long longitudinal dimension, or high aspect ratio of length to width, in order to achieve stability of a valve stem along its axial length.
Engine designers also consider the aspect ratio of the cup-type cam follower. The longitudinal dimension of a conventional cup-type cam follower assembly must be long enough to stabilize the cam follower along its axial length, therefore seeking to reduce the horizontal thrust exerted on the valve stem. As the cam lobe rotates and depresses the cup, the cup's resistance to the side thrust component is manifest in wear on the cup along a line 90.degree. from the axis of rotation of the cam lobe.
In a typical cup-type cam follower, the top of the cup or cup face must have sufficient diameter to cover the valve spring. This cup configuration, thus requires a cup wide enough to cover a valve spring and long enough to be stable. The requirement for large cup increases the overall size of the assembled engine.
Crankshafts
Typical single piece and modular crankshafts have suffered harmonic breakage problems. These problems occur when the natural frequency of vibration of the modular crankshaft matches the frequency of impulses applied to the crankshaft, resulting in breakage, or can induce intolerable torsional deflections of the crankshaft.
The typical high RPM engine produces power input pulses near the frequency range of the natural resonant frequency of the typical crankshaft. Thus, typical modular crankshafts tend to suffer from breakage as the input frequency matches the natural frequency of vibration. Typical modular and single piece crankshafts may also be distorted and strained from bending moments asserted on the crankshaft by the force of the pistons pushing the crankshaft pins.
Cam Shafts
Typical cam shaft deflection has caused typical engine designers to have problems synchronizing interconnected engine modules together to achieve appropriate timing. The cam shaft twists due to the twisting torque applied to it, adversely affecting the timing and the synchronization between engine modules. Typical engine designers utilize a large cam shaft to reduce twisting of the cam shaft in an attempt to overcome timing problems. Large typical cam shaft designs, however, increases the overall size and weight of the assembled engine.
Engine Assembly
Typical engine assembly utilizes a wide array of nuts, bolts and washers of varying shapes, sizes and lengths to assemble the parts to make a typical engine. The typical engine is assembled by different fasteners each having different torque requirements for each individual part of the engine. Different fasteners and different torque create a nonuniform stress gradient on the typical assembled engine. Nonuniform stress distorts the shape of the engine. Diversity of fasteners creates inventory overhead work for the engine manufacturer. The manufacturer must keep up with a wide variety of different size nuts and bolts. Thus, a wide variety of tools are required. Typical engines are assembled utilizing a different tool and assembly procedure for each part of the engine. Typical engines also utilize gaskets between metal parts which creates an assembled tolerance variation. Gaskets variably compress to a nonuniform thicknesses according to the pressure applied to the gasket. The pressure varies at each fastener and at each fastener location. Thus the tolerance of the assembled engine can vary as the thickness of the sealing gaskets vary.
When assembling modular engines designers have found that typical engines require a different size oil pump and cooling pump for each different modular engine configuration, depending upon the number of modules connected to construct the engine. Oil pump size varies with engine size. Thus, the manufacturer must supply a different size coolant and lubrication pump for each configuration of one, two, three, four, or five typical engine modules connected together to construct an engine.
Typically lubrication and coolant fluid flow serially through interconnected engine modules so that the lubricant and coolant fluid enter the first engine module where the fluid is pre-heated by the first engine module before the fluid enters the second engine module, third module, fourth module, and so on. Thus, the fluid entering the last engine module is substantially warmer than the fluid that entered the first engine module. Thus each typical interconnected engine modules run at a different temperature.
Pistons
Typical piston assemblies utilize a trunk style piston. The trunk piston has a flat circular top and a long cylindrical body or trunk. The trunk of the conventional piston fits closely within the cylinder. The cylinder wall guides the trunk of the piston and provides for stability of the piston along the longitudinal axis of the cylinder. The trunk of the conventional piston must be long enough, relative to the diameter of the piston, to provide adequate stability. The ratio of the piston length over the piston diameter determines how stable the motion of the piston is. The trunk of the piston rubs along the cylinder wall. The cylinder wall guides the piston. The additional weight of the elongated piston trunk increases the dynamic weight of the piston, thereby increasing the accelerative forces exerted on the piston, connecting rod and crankshaft pin.
Typical pistons such as the trunk type piston, increase the overall size of the engine because the length of the cylinder must accommodate the additional length of the conventional piston trunk plus the displacement of the connecting rods. The typical trunk type piston also suffers from thermal expansion problems. Metal expands when heated. The trunk type piston swells to a large diameter when heated. Thus, the cylinder must be large enough to allow passage of the enlarged heated piston. The cylinder diameter must be large enough to maintain a substantial clearance between the cylinder wall and the piston trunk over the full range of engine operating temperatures. The clearance between the outside diameter of the conventional trunk type piston and the internal diameter of the cylinder wall must be maintained at all operating temperatures or the piston will "seize up" in the cylinder. Thus, typically, a substantial gap exists between the piston trunk and the cylinder wall to allow for variations in the diameter of the piston over the full operating temperature range of the engine. This excess gap left to allow for swelling of the piston creates a problem. At lower temperatures, there is a large gap between the piston trunk and the cylinder wall. At higher temperatures, the gap-between the piston and the piston wall is very narrow. The gap between the cylinder wall and the piston trunk, varies widely over the operating range of the engine. Thus there is a variation in the stability of the piston along the longitudinal axis of the cylinder.
These thermal expansion considerations require engine manufacturers to design within close tolerances yet leave large gaps to account for wide variations in piston size over the operating temperature range. Piston stability along the longitudinal axis of the cylinder varies widely over the operating temperature range. Moreover, high tolerance requirements slow down the manufacturing process, to insure that the high tolerance is maintained. Slower manufacturing, requires additional man hours and time to produce the engine.
Connecting Rods
Typically connecting rods encircle and rotate around a crankshaft pin. The connecting rod end which attaches to the crankshaft pin must be a certain minimum width so that adequate lubrication can be established between the connecting rod end and the rotating crankshaft pin. Lubrication is in adequate below this minimum width causing increased wear and mechanical failure.
Typically engines utilize connecting rods which are open at one end and bolted to a semi circular connecting rod bracket to form a circle around a crankshaft pin. The two piece, nut and bolt connecting rod configuration requires considerable additional mass for the nuts and bolts, thereby increasing the dynamic weight and forces experienced by the crankshaft and connecting rod attached thereto.
The typical connecting rod requires considerable space. Although some engines attach more than one connecting rod to each crankshaft pin, typically the rods are side by side on a single crank pin. In this configuration, each connecting rod applies a sheer force across the entire crank pin length, a distance equal to twice the width of the connecting rod at the crank pin. The sheer force and attendant bending moment can cause bending and even breaking of the crankshaft pin.
Cylinder Head Seal
Some typical engines utilize a single piece head and cylinder assembly comprising a one-piece cylinder and cylinder head. This one-piece configuration presents a problem in machining the cylinder head. Machine bits must extend through the length of the cylinder to reach the machine surfaces of the attached cylinder head. Thus longer cutting bits must be used to reach the head. Longer bits are less rigid and thus reduce the accuracy of the head machining process.
Other engines utilize a separate cylinder and cylinder head. Engine assemblers seal the cylinder head to the cylinder formed in an engine block with large bolts and gaskets. Gaskets are subject to variable thickness, depending upon the amount of pressure applied at each bolt location which the gasket seals. Irregular tolerances in an assembled engine decreases the structural integrity of the assembled engine. For example, typically, head bolt assembly methods rely on high pressures at isolated fastener points which deforms the engine block and degredates the structural integrity of the engine. Typical head sealing methods require a complex bolt tightening pattern to exact torque requirements. Such a methodology is prone to irregular assembly.